Solving Linear Arithmetic Constraints for User Interface Applications: Algorithm Details

Authors: Alan Borning, Kim Marriott, Peter Stuckey, and Yi Xiao

Published as UW Tech Report 97-06-01.


Linear equality and inequality constraints arise naturally in specifying many aspects of user interfaces, such as requiring that one window be to the left of another, requiring that a pane occupy the leftmost 1/3 of a window, or preferring that an object be contained within a rectangle if possible. Current constraint solvers designed for UI applications cannot efficiently handle simultaneous linear equations and inequalities. This is a major limitation. We describe incremental algorithms based on the dual simplex and active set methods that can solve such systems of constraints efficiently. Both algorithms have been implemented and tested.

This informal technical report is adapted from the paper "Solving Linear Arithmetic Constraints for User Interface Applications," which will appear in the Proceedings of UIST'97 (The ACM User Interface and Software Technology Symposium). It contains additional details, in particular of the Cassowary and QOCA algorithms.

full tech report (compressed postscript)

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